1. Field of the Invention
The present invention relates generally to ceramic materials used to fabricate composite magnetic disk sliders for magnetic heads and used to fabricate other sliding parts subject to friction and wear. More particularly, the invention relates to a calcium titanate ceramic material for composite magnetic disc sliders with enhanced tribological characteristics that reduce both the wear and friction experienced in a magnetic head/disk interface thereby increasing the life of the slider and disk media.
2. Description of the Related Art
In magnetic head-supporting members (referred to as "sliders" hereinafter), it is desired to adapt the thermal expansion coefficient of the slider to that of the magnetic head supported by the slider by appropriately selecting the composition of the ceramic used to fabricate the slider.
Since the slider supports very small magnetic pole pieces, very precise machine processing is necessary when fabricating the slider. Accordingly, it is desirable that the material used for slider fabrication have excellent processability characteristics. In particular, it is required that the resistance against grinding (cutting) b low and that chipping resistance be excellent.
Solid lubricant characteristics for the head material are also desirable.
As the magnetic recording density of the magnetic storage disks increases, it is necessary to reduce the distance between the head and the disk surface, thus reducing the air cushion in the interface. This increases the frequency of head slider/disk impact during the use of the disk drive. To reduce the risk of wear associated with this impact and to improve start/stop conditions generally, it is well known to apply a lubricating material, such as a fluorocarbon, on the disk.
The lubricant applied needs to be of optimum thickness since too thick a lubricant causes interference with the head/disk interface and too thin a lubricant will cause excessive disk wear.
On the other hand, it is known that the surface of a magnetic head slider opposite the disk surface also influences the behavior with respect to the contact between head and disk which is a further reason that the materials used for disk sliders must be selected carefully.
It is well known to use, as pad materials, calcium titanate and barium titanate when fabricating composite heads because of the excellent mechanical properties and uniform structures of these ceramics. Calcium titanate is generally used in combination with a manganese zinc ferrite core material, because calcium titanate's thermal expansion coefficient is substantially equal to that of Mn-Zn ferrite (100 to 200.times.10.sup.-7 /C). A Barium titanate ceramic material is another well known material generally used in combination with a nickel zinc ferrite core material. Again, because of the substantially equal thermal coefficients of the ceramic and the core.
Unfortunately, it is also known that in components made of these materials chipping is readily caused at the machining step, load resistance is large at the grinding step, and therefore, these materials are defective in that their processability is poor.
Technology has also changed making the need for a composite ceramic material having both good processability characteristics and solid lubrication characteristics more important. Prior art heads used to fly over a disk after head speeds reached 2400 to 3600 RPM. Heads were taken off before discs were stopped and as a result there was no physical contact between heads and disks.
According to the new Winchester technology, heads land on the disks and then take off from the disks, so there is a significant amount of contact between these components. To reduce the friction and wear of the disks and head pads, disks are lubed in the problematic fluid manner referred to hereinbefore. Again, some type of solid lubricant to avoid too thin or too thick an application would be desirable since the requirement of monitoring and maintaining a controlled amount of lubricant could be avoided.
Accordingly, it would be desirable if a head pad material could be developed having an optimum quantity of lubricant to reduce the friction and wear between the head and disc and at the same time provide the ideal physical properties for cutting, lapping, and polishing of the head pad.
It would also be desirable if such material included calcium titanate because of the aforestated mechanical properties and uniform structures exhibited by calcium titanate.
One of ordinary skill in the art will be aware that a number of manufacturers make calcium titanate ceramic material for magnetic recording heads but that the desired characteristics set forth hereinabove do not exist. By way of example, Kyocera International, Inc. makes two calcium titanate ceramic materials, TO710 and TO715. The only difference between the performance specifications for the two materials is their thermal expansion coefficient. TO175 has a higher thermal expansion then TO710. This higher thermal expansion property is achieved in TO715 by the addition of some strontium oxide (SrO) in the ceramic material recipe.
Independently, it is well known that certain metal oxides, like SrO, ZrO and Y2O3 act as solid lubricants in certain temperature ranges. Accordingly, it would be desirable to combine a material exhibiting solid lubricant characteristics, in an optimal weight percent and functional in predetermined temperature ranges, to reduce friction and wear, while at the same time optimizing the physical properties of impact strength, fracture toughness, resistance to deformation, chipping and cracking, of the ceramic material.